This paper (see attached pdf below) from William R. Ware PhD from JOM, the Journal of Orthomolecular Medicine is interesting, as it gives various ferritin thresholds associated with disease. Scroll down to "Association and Thresholds of Ferritin Levels and the Risk of Various Diseases" (page 3).
The author points out, not only is the upper limit of the normal range for ferritin set by most labs dangerously high, but 50% averages may also be associated with some ferrotoxic diseases.
The "Ferritin Thresholds for Benefit in Iron Lowering Studies" found on page 4 documents the benefits of iron reduction and guidelines for optimal iron homeostasis. Interesting in this area is the benefit of a single blood donation for glucose tolerance, even in those with relatively low ferritin (average 75).
The author does not mention this, but every blood donation causes a brief (several days) but drastic drop in hepcidin, the bodies master iron transport hormone. This drop opens the floodgates for iron transport within the body, and may help re-balance iron loading in tissues. This supports the hypothesis blood ferritin may not be accurately indicative of iron loading of various tissues within the body, and even those without alarmingly elevated ferritin may benefit from occasional whole blood donation. The iron is in the red cells, so plasma and platelet donors do not get this benefit.
Annual or bi-annual bloodletting may have a substantial effect in health and longevity, particularly for those who live in countries where iron fortification is the norm. The post war baby-boom generation has been the first to live their entire lives under iron fortification, and though we're living longer, chronic disease is running quite rampant.